There has been a clear and felt need for a suitable pickup and transfer device for irregularly surfaced and/or different sized or shaped objects such as populated printed wiring boards (PWBs). The term "populated" refers to boards populated with electrical components. Accordingly, a pickup and transfer device will be described for use in conjunction with such PWB's, although those skilled in the art will recognize that the scope of the invention is not so limited.
Typically a plurality of individual printed wiring boards are cut from a master board by an x-y cutting machine that is part of an automated assembly line. One such cutting system is described in co-pending U.S. patent application Ser. No. 723,428, filed Apr. 15, 1985, and assigned to the assigness of the present application. The aforementioned application describes a fluid jet cutting system for cutting individual boards from a masterboard, and teaches that the fluid jet may advantageously be used to cut populated masterboards. By cutting the masterboards after component insertion, cleaning, etc., standardized tooling and other cost-reducing measures are possible.
The automatic pickup and transfer of populated printed wiring boards from one assembly line to another is highly desirable; however there have not been any commercially successful devices capable of reliably performing this labor-intensive task. This is particularly true if the pickup device must handle boards of varying topography and shape with minimal operator intervention. Additionally, it may also be important to maintain registration of the boards after the boards are transfered to facilitate their handling downstream.
Prior attempts to pick up populated printed wiring boards of variable size and shape have been limited to mechanical grippers. However, mechanical grippers must be positioned with respect to the edges of the board to be transferred. When a plurality of boards have been cut from a master board, and are to be removed from a platen, some of the edges may be blocked from the gripper by the adjacent edges of neighboring boards. Additionally, the movement of such grippers must be changed to accommodate changes in the shapes and sizes of the individual boards which may occur from one production run to the next.
Vacuum "grippers" are more flexible than mechanical grippers because they are less dependent on the specific locations of the boards' perimeters. In theory, a vacuum gripper can pick up a board so long as it makes contact with the board anywher along its surface. While vacuum devices have been generally useful for picking up and moving objects, the prior art vacuum devices require that the vacuum device (typically a suction cup) engage the object to be grasped around the entire periphery of the cup in order to provide an adequate seal and maintain a hold on the object. When a portion of the periphery fails to seal, owing to blockage by the edge of a component, for example, the resulting leakage weakens the hold so that the object may not be picked up or may be dropped before reaching its intended destination. Thus, while vacuum grippers are highly desirable, they have been limited to use with unpopulated PC boards, or similar objects with smooth surfaces.